This invention relates to determining, by nondestructive test methods, the purity of composition of bars of material of a given shape; and more particularly, to determining whether a bar of precious metal has a purity of composition which is within a given range of variance from that of a standard bar of known purity of composition.
U.S. Pat. No. 3,981,175, issued Sept. 21, 1976 (hereby expressly incorporated by reference), discloses an apparatus for making such a nondestructive determination, wherein a standard bar, of known purity of composition, and a sample bar, whose purity of composition is desired, are both placed in a thermal chamber. A heat pulse of finite duration is applied to one end of both bars and the temperature vs. time responses of the opposite ends of both bars are monitored to determine the similarity of response.
In a copending application "Improved Method of and Apparatus for Nondestructively Determining the Composition of an Unknown Material Sample" filed by Ogden H. Hammond III, is described an improved method and apparatus for sequential monitoring, wherein the heat pulse is first applied to one end of the standard bar and the temperature vs. time response of the other end of the standard bar is measured, at specified instants of time, and stored. One end of a sample bar is then subjected to the same heat pulse and the temperature of the other end of the sample bar is measured at the same specified instants of time, relative to the application of the heat pulse. The temperature responses of the two bars are then used to make a decision as to the purity of composition of the sample bar.
The principal object of the present invention is to provide an improved noncontact bar heater, which due to the absence of contact resistances, is capable of producing a constant specified amount of heat rise in different bars, in a short period of time.